The use of rectifier power diodes in a logical OR arrangement has been known for some time for supplying direct-current power from a plurality of power sources to one or more common loads. A long-standing problem in this area has been the difficulty of detecting failures of the power diodes without shutting down (that is, taking out of service) or incurring the risk of shutting down one or more of the loads.
In known ORed power distribution, such as is shown in FIG. 1 of the drawings herein, at least two separate power distribution buses are used with each separate bus being supplied with power from a separate power source, with each bus being connected through a separate fuse and a separate power diode so as to feed power to the same power terminal of at least one common load, and with the power sources and the common load having a common power supply return.
One known way of detecting failure of such power diodes is to turn off (that is, remove the power source from) each bus, one at a time, and to observe the consequences. An open power diode will cause the equipment it feeds to shut down as the opposite bus is turned off. If a power diode is shorted, one of at least two events will occur depending upon the amount of independent load supplied by the bus which is turned off. If the latter bus feeds only load connected through ORed power diodes, then a shorted power diode will not allow its associated bus voltage to drop very far when that bus is turned off. The problem then would be to ascertain which power diode on that bus is the one that is shorted and to do so without shutting down on-line equipment. If that bus feeds any substantial independent load in addition to the ORed load, then a fuse will be blown when that bus is turned off and the load associated with the shorted diode will be shut down.
As outlined above, periodic turning off of each of the two power buses separately will allow some degree of detection of failed power diodes, but only at the risk of shutting down on-line load equipment associated with a failed power diode. Also, in the latter regard, any load equipment independently supplied (that is, not commonly supplied from more than one bus through ORed power diodes) from a bus is also shut down during the test. Also, another problem attendant to such a test is the risk that rapid voltage and current transients associated with the bus turn-off and with the bus turn-on may introduce error signals.
For the foregoing reasons, and other reliability problems, it has not been common practice to provide turn-off capability for such power buses, thus leaving the art faced with solving the power diode failure detection problem by the tedious process of manually testing the various components of the system.